Tripod type constant velocity universal joint

ABSTRACT

A tripod type constant velocity universal joint comprises an outer joint member having three track grooves with roller-guiding surfaces opposing each other circumferentially, a tripod member with three trunnions protruding in a radial direction, a plurality of rollers each inserted into a corresponding track groove and a plurality of rings each fitted on the corresponding trunnion for supporting the roller rotatably. An outer surface of the trunnion is formed to take on a straight shape in a longitudinal section and an ellipse shape in a cross-section. A contact ellipse shape between the trunnion and the ring is modified so as to render the radius of curvature r smaller while keeping an aspect ratio b/a stable in comparison with a contact ellipse shape being defined to minimize contact pressure between a ring inner surface and a trunnion outer surface.

This application is a divisional of application Ser. No. 11/411,837, filed Apr. 27, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a tripod type constant velocity universal joint for use in a drive train of automobiles and other industrial machineries, and especially relates to tripod type constant velocity universal joints that expand a low vibration characteristics range of induction thrust to wider operating angles between two connected rotary shafts.

2. Description of the Background Art

A constant velocity universal joint is one of the universal joints that enables constant velocity linkage even if a driving shaft axis and a driven shaft axis make an operation angle. The constant velocity universal joints are classified as either fixed joint or sliding joint. A sliding joint enables relative axial displacement by a plunging behavior of a joint. Furthermore, a sliding joint includes a tripod joint which comprises a tripod member connected to an end of one shaft having three protruded trunnions in a radial direction, and a hollow shaped outer joint member connected to an end of another shaft having three track grooves that extend in an axial direction and trunnions of tripod members inserted to track grooves of an outer joint member to perform torque transmission.

The inventor of this invention has proposed tripod type constant velocity joints (hereinafter called as PTJ) to improve NVH (noise, vibration and harshness, hereinafter called as NVH) characteristics by free tilting movement of a roller to a trunnion. Reference is made to patent document 1 (Japanese Laid Open Publication 2000-320563) and patent document 2 (Japanese Laid Open Publication 2001-132766).

The PTJ as shown in FIG. 1 (A) and (B) comprises an outer joint member 10 and a tripod member 20, wherein one of two connecting shafts is connected with the outer joint member 10 and the other of the two connecting shafts is connected to the tripod member 20. The outer joint member 10 has three track grooves, which are extended in an axial direction on the inner surface of the joint body. A pair of roller-guiding surfaces 14 are formed in the opposite sidewalls of the track groove which are opposite to each other in a circumferential direction. The tripod member 20 has three trunnions 22 which protrude in a radial direction, each trunnion having a roller 34, with the roller 34 being inserted into a track groove 12 of the outer joint member 10. An outer surface of each roller 34 is a convex curved surface mating with a roller-guiding surface 14, with the outer surface of the roller 34 having a generating line which is an arc having a center of curvature being in alignment with or eccentric from an axis of the trunnion. A cross-section of the roller-guiding surface 14 is a gothic arc. Thus, the roller 34 and the roller-guiding surface 14 make an angular contact.

A ring 32 is fitted to an outer surface 22 a of each of the trunnions 22 as shown in FIG. 2. For each trunnion 22, a ring 32 and a roller 34 are unitized by plural needle rollers 36, and completed as a roller assembly that achieves relative rotation between the ring 32 and roller 34. A longitudinal section of the outer surface 22 a of the trunnions 22 looks cylindrical parallel to a trunnion 22 longitudinal axis as shown in FIG. 1A and FIG. 1B. Also, as shown in FIG. 2A and FIG. 3, a cross-section of a trunnion 22 is formed as an ellipse with a major axis being perpendicular to a joint axis, i.e., the thickness of the tripod member 20 in the axial direction is decreased to form an ellipse. In other words, opposing arced portions of the cross-section of the trunnion are recessed in an axial direction of the joint compared to a true cylindrical surface to form an ellipse.

An inner surface 32 a of the ring 32 is formed to have a convex arc R in a longitudinal direction as shown in FIG. 4A and FIG. 4B. Thus, a generating line of the inner surface 32 a is a convex arc having a radius r. With the convex arc, an ellipse cross-section of a trunnion 22 as explained above provides play between a trunnion 22 and a ring 32, with the ring 32 being not only movable in the axial direction of the trunnion 22, but also being pivotable on a trunnion 22.

The ring 32 and the roller 34 are assembled with the needle rollers 36 to allow relative rotation as described earlier, with the assembly including a ring 32 and a roller 34 being able to pivot on a trunnion 22. Hereinafter, pivoting is defined as a behavior in which an axis of ring 32 and roller 34 is inclined toward trunnion 22 within the plane that contains trunnion 22 axis and tripod member 20 axis. Refer to FIG. 1B.

By the above mentioned cross-section of the trunnion 22 and the cross-section of the ring 32, the trunnion 22 can tilt to the outer joint member 10 without changing a position of the roller assembly when the joint takes an operating angle θ. A friction moment which tends to incline a roller assembly can be reduced, because an area of contact ellipse made by a trunnion outer surface 22 a and a ring inner surface 32 a becomes smaller to lead the area to a small dot or circle. Therefore, orientation of a roller assembly becomes stable so that a roller rotates smoothly because of a parallel alignment of a roller and a roller guide surface. This construction can contribute to achieve lower slide resistance and induction thrust.

As described above, a contact plane of a trunnion outer surface of PIT and a ring inner surface becomes a contact ellipse. The area and shape of this contact ellipse is deeply related to joint induction thrust and slide resistance. Therefore, an optimum contact ellipse area and shape have been studied, but still satisfactory results have not been obtained yet.

A shape of contact ellipse is determined by an aspect ratio of minor axial length b to major axial length a of an ellipse section of a trunnion 22 and a radius of curvature r of convex R in a longitudinal section of a ring inner surface. Presently, each optimum figure of the aspect ratio b/a and a radius of curvature r are given to minimize the contact pressure. With the aspect ratio b/a and the radius of curvature r for minimizing contact pressure, it is possible to keep induction thrust and slide resistance low up to a certain operating angle, because a trunnion 22 and a roller assembly can be inclined relatively without inclination of a roller assembly to a roller-guiding surface of an outer joint member up to certain operating angle. However, it becomes clear that when the operating angle becomes greater than such certain operating angle, vibration characteristics get worse because the contact ellipse interferes with roller assembly movement. Therefore, simply increasing a maximum angle of inclination between a trunnion 22 and a roller assembly may deteriorate vibration characteristics, leading to durability getting worse due to an increase in contact pressure.

NVH problems of automobiles are solved effectively by making induction thrust and sliding resistance smaller. Generally, induction thrust and sliding resistance of joints depend on the degree of operating angle. This becomes a design restriction for effecting a larger operating angle when applied to drive shafts of automobiles.

The mission to have higher design freedom of automobile drive shaft system equipments are how low and stable induction thrust and slide resistance are obtained.

SUMMARY OF THE INVENTION

An object of this invention is to achieve further lower induction thrust and lower vibration by optimizing the shape of a contact ellipse between a trunnion and a ring of PTJ.

In order to solve this problem, the first aspect of the invention is to achieve such an object by a modifying radius of curvature r to be smaller while keeping the aspect ratio b/a stable.

The first aspect of the invention is directed to a tripod type constant velocity universal joint which includes an outer joint member having three track grooves, each of which has roller-guiding surfaces opposing each other in a circumferential direction; a tripod member with three trunnions protruding in a radial direction; a plurality of rollers each inserted into a corresponding track groove; a plurality of rings each fitted to the corresponding trunnion for enabling free rotation of the roller; each of the rollers being movable along with a roller-guiding surface in an axial direction of an outer joint member; an inner surface of the ring being formed as convex arc R in a longitudinal section; an outer surface of the trunnion taking on a straight shape in a longitudinal section and an ellipse shape in cross-section in order to render the outer surface thereof contiguous to an inner surface of the ring in a direction perpendicular to a joint axial direction and to form a play between a ring inner surface and an outer surface of trunnion in a joint axial direction; wherein a radius of curvature r is modified to be smaller while keeping the aspect ratio b/a stable.

To minimize the contact pressure between the ring inner surface and the trunnion outer surface of PTJ, it is presently thought that a contact ellipse should be close to a circle as far as possible as described in the patent document 1, paragraphs [0011] and [0025]. A conventional recommended value of the aspect ratio b/a and radius of curvature r is determined from such a viewpoint.

The inventor of the present invention comes to this invention without sticking to the conventional idea that is necessary to minimize contact pressure in which a contact ellipse shape is slightly elongated in a circumferential direction relative to an axial direction of the trunnion so that an operating angle of the joint can be widened while keeping induction thrust and vibration lower level.

The second aspect of the invention is directed to the tripod type constant velocity universal joint according to the first aspect of the invention wherein the radius of curvature r is within the range of 1.9a to 2.5a, and the aspect ratio b/a rs within the range of 0.8 to 0.9. The aspect ratio b/a is as stable as that of a conventional PTJ. The present invention renders the radius of curvature r short while keeping the aspect ratio stable.

As stated above, this invention provides a low vibration characteristics to a PTJ of wide operating angle with induction thrust to be under a certain value effected by the contact ellipse shape which is elongated in the circumferential direction of the trunnion by solely decreasing a radius of curvature r of the ring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of a tripod type constant velocity universal joint in accordance with an embodiment of the invention.

FIG. 1B is a longitudinal sectional view of a tripod type constant velocity universal joint when inclined to an operating angle θ.

FIG. 2A is a cross-sectional view of a trunnion with a roller assembly.

FIG. 2B is a longitudinal sectional view of a ring.

FIG. 3 is an enlarged cross-sectional view showing an aspect ratio of the trunnion.

FIG. 4A is a cross-sectional view of a ring.

FIG. 4B is a plan view of a ring.

FIG. 5 is a table showing analysis results of an induction thrust mechanism.

FIG. 6 is a graph showing analysis results of an induction thrust mechanism.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the present invention are given by referring to the drawings. A structure of a tripod type constant velocity universal joint of this invention is as shown in FIG. 1 through FIG. 4. Aforementioned explanations of FIG. 1 through FIG. 4 are the same to this invention and to be applicable to this invention. A novel feature of this invention lies in the combination of the aspect ratio b/a of trunnion cross-section shown in FIG. 3 and the radius of curvature r of convex R in a longitudinal section of ring inner surface as shown in FIG. 4.

PTJ transmits torque by contacting an ellipse shaped trunnion 22 and a ring 32 with an inner surface as convex surface R, so a relaxation consideration of contact pressure of both parts is required. As to the relaxation of contact pressure, the patent document I defines a contact ellipse shape with r=2.9a and b/a=0.86 in the case of an operating angle of 15 degrees. (Refer to Table 1 of patent document 1.) When the operating angle is enlarged from 15 degrees to 17 degrees, according to the theory of patent document 1, both reverse aspect ratio b/a and radius of curvature r are required to be reduced. This is therefore Table 1 in the patent document 1 which defines r=1.994a and b/a=0.806 in the case of an operating angle of 20 degrees. On the contrary, the present invention achieves lower induction thrust by only decreasing of the radius of curvature r. Because decreasing the radius of curvature r makes less area decrease of the contact ellipse, the increase of contact pressure at an enlarged operating angle compared with the case where both radius of curvature r and reverse aspect ratio b/a are reduced.

From the simulation results obtained by mechanism analysis software, the case where both radius of curvature r and reverse aspect ratio b/a are made smaller, and the case where only reverse aspect ratio b/a is reduced cannot make lower the induction thrust at a higher operating angle range, however the case where radius of curvature r is smaller can contribute to lower induction thrust at a higher operating angle range.

FIG. 5 shows the summary of these analyses results. In FIG. 5, the conventional example is the case that the table 1 in the patent document 1 defines. Comparison example 1 shows the results of reverse aspect ratio being smaller, and comparison example 2 shows the results of radius of curvature r being smaller. The results of mechanism analyses show both cases do not provide sufficient low results of induction thrust values. On the contrary, the embodiment of the present invention, which makes smaller the radius of curvature r, provides sufficient low induction thrust in a high operating angle range. In this embodiment, the reverse aspect ratio is set as 0.86 as conventional example and reduction in radius of curvature r from 2.9a to 2.1a.

FIG. 6 shows the simulation results in a chart. In this chart, a dotted line shows comparison examples 1 and 2. A solid line shows the embodiment of the invention. Assuming that the allowable upper limit of induction thrust component is 20 N, this embodiment realizes the high operating angle that is no less than 2 degrees wider than the comparison examples.

The constant velocity universal joint of this invention can be applied advantageously to automobile drive shafts in order to provide better NVH characteristics of automobiles influenced by the induction thrust and slide resistance together with increased design freedom of automobile drive shaft system design. 

1-2. (canceled)
 3. A method of forming a tripod type constant velocity universal joint, wherein the tripod type constant velocity universal joint includes: an outer joint member having three track grooves, each of the track grooves having a pair of roller-guiding surfaces opposing each other in a circumferential direction; and a tripod member having three trunnions protruding in a radial direction, the method of forming the tripod type constant velocity universal joint comprising: inserting a plurality of rollers into a corresponding one of the track grooves, each of the rollers being movable in an axial direction of the outer joint member along the corresponding pair of roller-guiding surfaces; fitting each of a plurality of rings on a corresponding one of the trunnions for rotatably supporting one of the rollers, an inner surface of each of the rings being formed as a convex arc R in longitudinal section; forming, for each of the trunnions, an outer surface of the trunnion to take on a straight shape in a longitudinal section and an ellipse shape in a cross-section to render the outer surface thereof contiguous to the inner surface of the corresponding ring in a direction perpendicular to a joint axial direction and to provide play between the inner surface of the ring and the outer surface of the trunnion in the joint axial direction; and modifying, for each of the trunnions, a contact ellipse shape between the trunnion and the corresponding ring so as to render a radius of curvature r smaller while keeping an aspect ratio b/a stable in comparison with the contact ellipse shape being defined to minimize contact pressure between the inner surface of the ring and the outer surface of the trunnion, wherein r is a radius of curvature r of the convex arc R in a longitudinal section of the inner surface of the ring, a is a major axial length of trunnion cross-section ellipse, b is a minor axial length of trunnion cross-section ellipse, and b/a is an aspect ratio of trunnion cross-section.
 4. The method of forming a tripod type constant velocity universal joint according to claim 3, wherein the radius of curvature r is from 1.9a to 2.5a, and the aspect ratio b/a is from 0.8 to 0.9. 